How to buy storage

Editors' note: This article is frequently updated to reflect changes in technology and in the marketplace.

The computing world runs on information, and handling it is crucial. So it's important that you select the best storage device to not only hold your data, but also distribute it. In this guide, I'll explain the basics of storage and list the features that you should consider when shopping. If you're ready to head to the store right now, though, I've also listed my top picks.

Power users hoping to get the most out of a home storage system should consider a network-attached storage (NAS) server such as a four- or five-bay NAS server from Synology, QNAP, Asus, Netgear, Western Digital or Seagate. Alternatively, if you want your new computer to run at its top speed, a solid-state drive (SSD) such as the Samsung 850 Pro or the Toshiba OCZ VX500, or an M.2 drive (if your computer supports it) will make that happen. But if you have an older machine and budget is an issue, there are more affordable SSDs, like the Samsung SSD 850 Evo or the OCZ Trion.

There are three main areas you should consider when picking a storage device: performance, capacity and data safety. I'll explain them briefly here. After you're finished, I encourage you to check out this article for an even deeper dive into the world of storage.

Using an SSD like one of these will greatly improve your computer's performance.

Dong Ngo/CNET

Performance

Storage performance refers to the speed at which data transfers within a device or from one device to another. Currently, the speed of a single consumer-grade internal drive is largely defined by the Serial ATA interface standard (SATA). This determines how fast internal drives connect to a host (such as a personal computer or a server) or to one another. There are three generations of SATA -- the latest and most popular, SATA 3, caps at 6 gigabits per second (about 770 megabytes per second). The earlier SATA 1 (largely obsolete) and SATA 2 standards cap data speeds at 1.5Gbps and 3Gbps, respectively.

So what do those data speeds mean in the real world?

Consider this: At top speed, a SATA 3 drive can transfer a CD's worth of data (about 700MB) in less than a second. The actual speed of a hard drive may be slower because of mechanical limitations and overheads, but that should give you an idea of what's possible. A hard drive's real-world speed tends to be around one-tenth of the SATA 3 standard. SSDs, on the other hand, offer speeds much closer to the SATA 3 ceiling. Most existing internal drives and host devices (such as computers) now support SATA 3, and are backward-compatible with previous revisions of SATA.

Since 2015, there's been a new standard called M.2, which is only available for SSDs. M.2 allows the storage device to connect to a computer via PCI express (the type of connection once used only to connect a video card to a motherboard) and is therefore much faster than SATA. Currently, only high-end desktop motherboards support M.2. These tend to come with two slots. Some ultracompact laptops also have an M.2 slot instead of SATA. Just about the size of a stick of system memory, an M.2 SSD is much more compact than a regular SSD. It's also much faster and can deliver the same amount of storage space. In the future, M.2 is expected to replace regular SATA drives completely.

Since internal drives are used in most other types of storage devices, including external drives and network storage, the SATA standard is the common denominator of storage performance. In other words, a single-volume storage device -- one that has only one internal drive inside -- can be as fast as 6Gbps. In multiple-volume setups, there are techniques that aggregate the speed of each individual drive into a faster combined data speed, but I'll discuss that in more detail in the RAID section below.

Capacity

Capacity is the amount of data that a storage device can handle. Generally, we measure the total capacity of a drive or a storage system in gigabytes. On average, 1GB can hold about 500 iPhone photos or about 200 iTunes songs.

Currently, the highest-capacity 3.5-inch (desktop) internal hard drive can hold up to 10 terabytes (TB) or roughly 10,000GB. On laptops, the top hard drives as well as SSDs can offer up to 2TB.

While a single-volume storage device's capacity will max out at some point, there are techniques that make it possible to combine several drives to offer dozens of TBs and even more. I'll discuss that in more detail as well in the RAID section below.

The Glyph Blackbox Plus portable drive.

Dong Ngo/CNET

Data safety

The safety of your data depends on the durability of the drive on which it's stored. And for single drives, you have to consider both the drive's quality and how you'll use it.

Generally, hard drives are more susceptible to shocks, vibration, heat and moisture than SSDs. Durability isn't a big issue for a desktop since you won't be moving your computer very often (one hopes). For a laptop, however, I'd recommend an SSD or a hard drive that's designed to withstand falls and other sudden movement.

When it comes to portable drives, you can opt for a product that comes with layers of physical protection, such as the Glyph Blackbox Plus or the G-Tech G-Drive ev ATC. These drives are generally great for people working in rough environments.

But even when you've chosen the optimal drive for your needs, you mustn't forget to use backup, redundancy or both. Not even the best drive is designed to last forever -- and there's no guarantee against failure, loss or theft.

The easiest way to back up your drive is to regularly put copies of your data on multiple storage devices. Most external drives come with automatic backup or sync software for Windows. Mac users, on the other hand, can take advantage of Apple's Time Machine feature. All external drives work with both Windows and Macs, as long as they're formatted in the right file system: NTFS for Windows or HFS+ for Macs. The reformatting takes just a few seconds. If you're on a budget or want to quickly find the best portable storage system, here's our list of top portable drives.

But be warned -- this process isn't foolproof yet. Besides taking time, backing up your drive can leave small windows in which data may be lost. That's why for professional and real-time data protection, you should consider redundancy.

RAID

The most common approach to data redundancy is RAID, which stands for "redundant array of independent disks." RAID requires that you use two internal drives or more, and depending on the setup, a RAID configuration can offer faster speeds, more storage space or both. Just note that standard RAIDs generally require drives of the same capacity. Here are the three most common RAID setups.

RAID 1: Also called mirroring, RAID 1 requires at least two internal drives. In this setup, data writes identically to both drives simultaneously, resulting in a mirrored set. What's more, a RAID 1 setup continues to operate safely even if only one drive is functioning (thus allowing you to replace a failed drive on the fly). The drawback of RAID 1 is that no matter how many drives you use, you get the capacity of only one. RAID 1 also suffers from slower writing speeds.

RAID 0: Like RAID 1, RAID 0 requires at least two internal drives. Unlike RAID 1, however, it combines the capacity of the drives into a single volume while delivering maximum bandwidth. The only catch is that if one drive dies, you lose information on all devices. So while more drives in a RAID 0 setup means higher bandwidth and capacity, there's also a greater risk of data loss. Generally, RAID 0 is used mostly for dual-drive storage setups. And should you choose RAID 0, backup is a must. RAID 0 is the only RAID setup that doesn't provide data protection.

For a storage device that uses four internal drives, you can use a RAID 10 setup, which is the combination of RAID 1 and RAID 0, for both performance and data safety.

RAID 5: This setup requires at least three internal drives, but it distributes data on all drives. Though a single-drive failure won't result in the loss of any data, performance will suffer until you replace the broken device. Still, because it balances storage space (you lose the capacity of only one drive in the RAID), performance and data safety, RAID 5 is the preferred setup.

RAID 6: This array is similar to RAID 5, but now the array can survive the case that two of its internal drive fails at the same time. RAID 6 is generally used in storage devices that have 5 internal drives or more. In a RAID 6, you lose the capacity of two internal drives.

Most RAID-capable storage devices come with the RAID setup pre-configured, so you don't need to set that up yourself.

Now that you've learned how to balance performance, capacity and data safety, let's consider the three main types of storage devices: internal drives, external drives and network-attached storage (NAS) servers.

Internal drives

Though they share the same SATA interface, the performance of internal drives can vary sharply. Generally, hard drives are much slower than SSDs, but SSDs are much more expensive than hard drives, gigabyte for gigabyte.

That said, if you're looking to upgrade your system's main drive -- the one that hosts the operating system -- it's best to get an SSD. You can get an SSD with a capacity of 256GB (currently costing around $150 or less), which is enough for a host drive. You can always add more storage with an external drive or, in the case of a desktop, another regular secondary hard drive.

External drives

External storage devices are basically one or more internal drives put together inside an enclosure and connected to a computer using a peripheral connection.

There are four main peripheral connection types: USB, Thunderbolt, FireWire and eSATA. Most, if not all, new external drives now use just USB 3.0 or Thunderbolt or both. There are good reasons why.

USB 3.0 offers a cap speed of 5Gbps and is backward-compatible with USB 2.0. Thunderbolt caps at 10Gbps (or 20Gbps with Thunderbolt 2.0), and you can daisy-chain up to six Thunderbolt drives together without degrading the bandwidth. Thunderbolt also makes RAID possible when you connect multiple single-volume drives of the same capacity. Note that more computers support USB 3.0 than Thunderbolt, especially among PCs. All existing computers support USB 2.0, which also works with USB 3.0 drives (though at USB 2.0 data speeds).

Generally, speed is not the most important factor for non-Thunderbolt external drives. That may seem counterintuitive, but the reason is that the USB 3.0 connectivity standard, which is the fastest among all non-Thunderbolt standards, is slower than the speed of SATA 3 internal drives.

Capacity, however, is a bigger issue. USB external drives are the most affordable external storage devices on the market, and they come with a wide range of capacities to fit your budget. Make sure to get a drive that offers at least the same capacity as your computer. Check out our list of best external drives for more information.

There's no difference in terms of performance between bus-powered (a data cable is also used to draw power) and non-bus-powered (a separate power adapter is required) external drives. Generally, only single-volume external drives that are based on a laptop 2.5-inch internal drive can be bus-powered, and these drives offer around 2TB of storage space. Non-bus-powered external storage devices mostly use 3.5-inch internal drives and can combine multiple internal drives, so they can offer more storage space.

Currently, Thunderbolt storage devices are more popular for Macs, and unlike other external drives, deliver very fast performance. They are significantly more expensive than USB 3.0 drives with prices fluctuating a great deal depending on the number of internal drives you use. Here's our list of the top Thunderbolt drives.

Network-attached storage (NAS) devices

A NAS device (aka NAS server) is very similar to an external drive. But instead of connecting to a computer directly, it connects to a network and offers storage space to all devices on the network at the same time.

As you might imagine, NAS servers are ideal for sharing a large amount of data between devices. Besides storage, NAS servers offer many more features, like being capable of streaming digital content to network players, downloading files, backing up files from a network computer and sharing data over the internet.

If you're in the market for a NAS server, you should focus on the capacities of the internal drives used. Also, it's a good idea to get hard drives that use less energy and are designed to work 24-7 since NAS servers are generally left on all the time.

Connection types

A final consideration when purchasing a storage device is the connection. Currently, it all comes down to USB vs. Thunderbolt, since other types are largely obsolete. Obviously you'll want to get a drive that can work with your computer. So if your machine has a Thunderbolt or Thunderbolt 2 port (as most Macs do) then you'll want to get a Thunderbolt drive. On the other hand, since most computers have at least one USB port, getting a USB-based drive is a safe bet. Some portable drives support both Thunderbolt and USB.

However, if you want your drive to be future-proof -- meaning it will not only work with your current computer, but also the computer you'll buy a year or three from now -- then you need one with a USB-C port. A USB-C portable drive will work with all existing computers when you use a USB-C-to-USB-A cable. If you have a computer that has a USB-C port, such as the MacBook, you can connect a USB-C drive to it by using a regular USB-C-to-USB-C cable.

Currently, all new computers with Thunderbolt will also support USB-C. This is because the latest version of Thunderbolt 3 has moved to use the same port type and cable as those of USB-C. In other words, every Thunderbolt 3 port will also function as a normal USB-C port and every Thunderbolt 3 cable will also work as a USB-C cable.